This invention relates to timing circuitry, and more particularly to circuitry which commences its timing cycle when external power is removed. At the end of the timing cycle current is switched through a load.
This type of circuitry has utility in detonating explosives and will be described in that context. In quarry mining, for example, explosive charges are placed in holes that are drilled in the strata in predetermined configurations to produce shock waves that make most efficient use of the explosives. In order to generate the desired shock wave, the charges are detonated in a particular sequence. Heretofore, the sequencing has been accomplished by basically two methods. The first method utilizes a master console to which all of the charges are wired. The console is then programmed to electrically detonate the charges in the desired sequence. This method, although it provides precise detonation timing, promotes its own malfunction due to first explosions disturbing electrical connections to non detonated charges. The second method employs detonators which provide a combination of electrical ignition, and a chemical delay, e.g. variable length fuses. In this instance each of the charges are simultaneously primed electrically and the detonation sequence is thereafter produced by the varying length of chemical delay built into each charge. Detonation of later charges is rarely affected by the first detonated charges, however, the sequencing is far less precise.